Rotary stirring device for treating molten metal

Abstract

Rotary device for treating molten metal has a hollow shaft with a rotor having a roof and a base spaced apart and connected by a plurality of dividers. A passage extends between each adjacent pair of dividers and the roof and the base. A flow path extends through the shaft into inlets of the passages and out of outlets. A chamber in which mixing of the molten metal and gas can take place is located radially inwardly of the inlets, has an opening in the base of the rotor and is in the flowpath between the shaft and the inlets. Upon rotation of the device, molten metal is drawn into the chamber through the rotor base where it is mixed with gas passing into the chamber from the shaft. The metal/gas dispersion is pumped into the passages through the inlets before discharge from the rotor through the outlets.

1. A rotary device for treating molten metal, said device comprising a hollow shaft at one end of which is a rotor, said rotor having:—
 a roof and a base, said roof and base being spaced apart and connected by a plurality of dividers; 
 a passage being defined between each adjacent pair of dividers and the roof and the base, each passage having an inlet in an inner surface of the rotor and an outlet in a peripheral surface of the rotor, each outlet having a greater cross-sectional area than the respective inlet and being disposed radially outward therefrom; 
 a flow path being defined through the shaft into the inlets of the passages and out of the outlets; and 
 a chamber in which mixing of the molten metal and gas can take place wherein the chamber is located radially inwardly of the inlets and has an opening in the base of the rotor and is in the flowpath between the shaft and the inlets, such that in use when the device rotates, molten metal is drawn into the chamber through the base of the rotor where it is mixed with gas passing into the chamber from the shaft, the metal/gas dispersion then being pumped into the passages through the inlets before being discharged from the rotor through the outlets; 
 wherein a plurality of first cut-outs are provided in the roof and a plurality of second cut outs are provided in the base, each of the first and second cut outs being contiguous with one of the passages. 
 
     
     
       2. A rotary device as claimed in  claim 1 , wherein each first cut-out extends inwardly from the outer peripheral surface of the rotor and is contiguous with an outlet. 
     
     
       3. A rotary device as claimed in  claim 2 , wherein the extent of each first cut-out in the peripheral surface is no more than that of the corresponding outlet. 
     
     
       4. A rotary device as claimed in  claim 1 , wherein each first cut-out is part-circular and the first cut-outs are arranged symmetrically around the rotor. 
     
     
       5. A rotary device as claimed in  claim 1 , wherein the second cut-outs have the same size and shape as the first cut-outs. 
     
     
       6. A rotary device as claimed in  claim 1 , wherein the number of first cut-outs is equal to the number of second cut-outs. 
     
     
       7. A rotary device as claimed in  claim 1 , wherein the rotor has three, four or five passages. 
     
     
       8. A rotary device as claimed in  claim 7 , wherein the rotor has four passages. 
     
     
       9. A rotary device as claimed in  claim 1 , wherein the rotor has exactly one outlet and exactly one each of the first and second cut-outs per passage. 
     
     
       10. A rotary device as claimed in  claim 1 , wherein the rotor has exactly one outlet, and exactly two first cut-outs and two second cut-outs per passage. 
     
     
       11. A rotary device as claimed in  claim 6 , wherein each first cut-out in a passage is in full register with the corresponding second cut-out. 
     
     
       12. A rotary device as claimed in  claim 1 , wherein the first and/or second cut-outs extend inwardly no further than 50% of the radius of the rotor. 
     
     
       13. A rotary device as claimed in  claim 1 , wherein the first and/or second cut-outs extend inwardly no less than 10% of the radius of the rotor. 
     
     
       14. A rotary device as claimed in  claim 1 , wherein the peripheral surface of the rotor in a plane orthogonal to the shaft axis is nominally a circle, and the ratio of the length of the arc of the circle circumference removed in the roof by the first cut-out or cut-outs or removed in the base by the second cut-out or cut-outs contiguous with a given passage multiplied by the number of passages, to the circumference of the circle is at least 0.3. 
     
     
       15. A rotary device as claimed in  claim 14 , wherein the ratio is no more than 0.9. 
     
     
       16. A rotary device as claimed in  claim 1 , wherein the shaft and rotor are formed separately, the two being attached together by releasable fixing means. 
     
     
       17. A rotor for use in the rotary device of  claim 1 , said rotor having a roof and a base, said roof and base being spaced apart and connected by a plurality of dividers;
 a passage being defined between each adjacent pair of dividers and the roof and the base, each passage having an inlet in an inner surface of the rotor and an outlet in a peripheral surface of the rotor, each outlet having a greater cross-sectional area than the respective inlet and being disposed radially outward therefrom; 
 a flow path being defined through the inlets of the passages and out of the outlets; and 
 a chamber in which mixing of the molten metal and gas can take place wherein the chamber is located radially inwardly of the inlets and has an opening in the base of the rotor and is in the flowpath between the shaft and the inlets, such that in use when the device rotates, molten metal is drawn into the chamber through the base of the rotor where it is mixed with gas passing into the chamber from the shaft, the metal/gas dispersion then being pumped into the passages through the inlets before being discharged from the rotor through the outlets; 
 wherein a plurality of first cut-outs are provided in the roof and a plurality of second cut outs are provided in the base, each of the first and second cut outs being contiguous with one of the passages. 
 
     
     
       18. A metal treatment unit for degassing and/or for addition of metal treatment substances comprising the rotary device of  claim 1 . 
     
     
       19. A method of treating molten metal comprising the steps of:—
 (i) immersing the rotor and part of the shaft of the rotary device of  claim 1  in the molten metal to be treated, 
 (ii) rotating the shaft, and 
 (iii) passing gas and/or one or more treatment substances down the shaft and into the molten metal via the rotor and/or passing one or more treatment substances directly into the molten metal, whereby to treat the metal. 
 
     
     
       20. The method of  claim 19 , wherein the metal being treated is selected from aluminium and its alloys, magnesium and its alloys and copper and its alloys. 
     
     
       21. The method of  claim 19 , wherein the gas passed in step (iii) is a dry inert gas. 
     
     
       22. A rotary device as claimed in  claim 12 , wherein the first and/or second cut-outs extend inwardly no further than 40% of the radius of the rotor. 
     
     
       23. A rotary device as claimed in  claim 13 , wherein the first and/or second cut-outs extend inwardly no less than 20% of the radius of the rotor. 
     
     
       24. A rotary device as claimed in  claim 14 , wherein the ratio is at least 0.6.